Electrical braking for a d.c. servo motor control circuit

ABSTRACT

A circuit is disclosed for controlling operation of a DC shunt field motor that is utilized to drive a variable load, and stop the motor so that the load is accurately positioned at a preselected location. Logic circuitry controls the motor speed to a regulated low speed when the load approaches the desired location. An integrator circuit controls application of dynamic braking to stop the motor when the load is correctly located.

United States Patent 1 1 Pearson [54] ELECTRICAL BRAKING FOR A D.C.

SERVO MOTOR CONTROL CIRCUIT [75] Inventor: Samuel Reader Pearson,Farmers Branch, Tex.

. [73] Assignee: Texas Instruments Incoporated, Dallas, Tex.

[22] Filed: Jan. 5, 1971 [21] App]. No.: 103,967

[52] US. Cl. ..3l8/6l2, 318/594, 318/374, 318/375, 318/467 [51] Int. Cl...G05b 5/01 [58] Field of Search ..318/594, 612, 613, 616, 331, 318/374,375, 467

[5 6] References Cited UNITED STATES PATENTS Young ..31s 331 x Agin etal...... ..318/6l2 Kilt i- POWER on CLEAR )3 Y c i ON DELAY OJ LOW SPEED LOGIC SPREADER LATCH 1 Mar. 27, 1973 OTHER PUBLICATIONS IBM Tech.Disclosure, Vol. 11, No. 12, May 1969, pg. 1697, G. J. Agin.

Primary Examiner-T. E. Lynch AttorneyJames 0. Dixon, Andrew M. Hassell,Harold Levine, Melvin Sharp, Michael A. Sileo, Jr., Henry T. Olsen, GaryC. Honeycutt, Richard L. Donaldson and John E. Vandigriff [57] ABSTRACTA circuit is disclosed for controlling operation of a DC shunt fieldmotor that is utilized to drive a variable load, and stop the motor sothat the load is accurately positioned at a preselected location. Logiccircuitry controls the motor speed to a regulated low speed when theload approaches the desired location. An integrator circuit controlsapplication of dynamic braking to stop the motor when the load iscorrectly located.

8 Claims, 1 Drawing Figure ELECTRICALBRAKING FOR A DC SERVO MOTORCONTROL CIRCUIT BACKGROUND INFORMATION AND SUMMARY OF INVENTION Thisinvention pertains in general to high speed positioning systems and,more particularly, to a motor control circuit for a DC shunt fieldmotor.

Various applications in industry require high speed positioning meansfor accurately positioning a load having a variable inertia andmechanical resistance. In some environments, it is desirable to effectthe positioning without utilizing servo-type feedback systems. Onetechnique that has been proposed to accomplish this uses a DC shuntfield motor. A regulated voltage is applied to the motor to slow itsspeed prior to applying dynamic braking to stop the load. A majordisadvantage with this technique is the fact that the speed of motoroperation is a function of the load mechanical resistance. Thus, whendynamic braking is applied to stop the load, accurate positioning of theload is difficult since the final position is influenced by both theinertia and mechanical resistance of the load.

The requirement for a high speed positioning system that accuratelylocates a load having a variable mechanical resistance is particularlyacute in automatic data retrieval and display systems of the type thatare comprised of a desk top, self-contained microfische file reader. Arotary storage file provides microfische storage for the internal fileof the system. When it is desired to view a preselected microfische, thecode of that microfische is entered via a keyboard and a view button isactivated to initiate a view cycle. Electromechanical relays and logiccircuitry are thereby activated to control operation of the file so thatthe desired microfische may be selected. When the desired microfische isrotated to a position adjacent to the display means, additionalcircuitry is activated to apply dynamic braking and stop the file suchthatthe desired microfische is accurately located at a predeterminedposition, spread the microfische apart so that the desired microfischeis exposed for easy access, and to automatically position themicrofische to an index display position. Each microfische, for example,may have 98 separate frames of microfilm. The index position cataloguesthe contents of the other 97 frames. From this index, the user canselect the frame he wishes to view and enter the coordinate location ofthat frame via a second keyboard to control servo motors that positionthe microfische so that the desired frame is displayed.

In the above-described display system, a DC motor control circuit isrequired to rotate the rotary file at a maximum speed until the desiredmicrofische is selected, slow the rotary file to a regulated speed andthen accurately stop the rotary file so the selected microfische may beretrieved. Inasmuch as the load (mechanical resistance) of the filevaries depending upon the number of microfische stored therein, it isdifficult to accurately stop the file at a preselected location.

Accordingly, an object of the present invention is to provide a highspeed motor control circuit that accurately positions a load havingvariable mechanical resistance.

A further object of the present invention is to provide a circuit forvariably controlling the speed ofa DC shunt field motor to accuratelyposition an object to a preselected location with maximum speed.

Briefly and in accordance with the present invention, a DC motorcontroller circuit is provided. Three main sections are utilized in thecircuit; a logic and control section, a regulated drive section, and anintegrator section. When full wave rectified 60 H drive is utilized,

the time required for motor time constants may be too long for 120 H,sampling, and it may be desirable to utilize a multivibrator section toeffectively reduce the cycle time to 60 H The logic and control systemcontrols operation of the motor for full speed, regulated speed orprogrammed stop. When full speed operation is desired, the control meansenable application of maximum drive power. When regulated speed isrequired, the control means effect immediate dynamic braking. Regulatormeans sense the actual motor speed during low voltage phases of thedrive power and apply the appropriate drive power during high voltagephases to maintain a preselected regulated low speed.

Responsive to a stop signal from the logic and control means, the speedintegrator section converts the motor speed signal from the regulatormeans to distance using a voltage to current converter. The integratormeans control application of dynamic braking to ensure the motor isaccurately stopped at the desired location.

Novel features believed to be characteristic of this invention are setforth in the appended claims. The in vention itself, however, as well asother objects and advantages thereof may best be understood when read inconjunction with the following detailed description of an illustrativeembodiment by reference to the accompanying drawing which schematicallydepicts the DC motor control circuit of the present invention.

DETAILED DESCRIPTION The DC motor control circuit and operation thereofwill first be described. An illustrative embodiment of the invention asit functions in an automatic data retrieval and display system will thenbe described. It is to be appreciated, of course, that the circuit ofthe present invention may be utilized whenever it is desired to switch aDC shunt field motor from high speed operation to a regulated low speedand then stop the motor at a precise position.

With reference now to the FIGURE, operation of the DC motor controlcircuit will be described. The DC motor drive circuit may be separatedgenerally into four functions or modes of operation: (1) full speed, (2)regulated low speed, (3) regulated low speed delay, and (4) stop. Inputsat terminals A and B control the mode of operation as follows:

When input A is at logic 1 and input B is at logic 0, maximum drivepower is applied to the motor. When both inputs are at logic 1, themotor is controlled to operate at a regulated low speed. When input Agoes to logic 0, and input B remains at logic 1, the circuit operates inthe delay mode and measures a predetermined distance of motor rotation,after which the circuit operates in the stop mode.

When input A is a l and input B is a 0, maximum drive power is appliedby the drive circuitry. The positive input at A is conducted throughresistor R54 to the base of npn transistor Q29. This saturates Q29reducing the voltage across capacitor C19 to a value at or near groundpotential, thus biasing pnp transistor Q28 off, which in turn biases npntransistor Q30 off effecting a DC voltage (+V) or logic 1 at thecollector of Q30 and the junction of resistor R61 and diode CR34. Thepositive voltage of logic 1 at the collector of Q30 is conducted throughresistor R53 to the base of npn transistor Q16. in addition, a signal isprovided at the output C to indicate that the DC motor M1 is receivingdrive power. Since input A is more positive than input B, and sinceresistors R53, R52 and R51, transistors Q16, Q15, Q13 and Q14 operate asa DC isolator, Q15 and Q16 will turn on providing drive through resistorR48 and diode CR8 to the base of pnp transistor Q19 and npn transistorQ18. This drive saturates transistor Q18 and provides maximum +V 1 driveto the DC motor M1. For a more detailed description of the DC isolator,reference copending application Ser. No. 103,965, filed l-7l, entitledDC lsolator Circuit, filed concurrently herewith and assigned to thesame assignee. At each cycle of the plus and minus power supplies, +V 1and -V,, pnp transistor Q24 will saturate through the action of resistorR227 which is connected to the minus power supply. This causes a voltageproportional to the motor speed to be stored in capacitors C17 and C16.An enable signal may be provided at input D to control drive throughresistor R53.

When input B also goes to a logic 1, a regulated slow speed mode ofoperation results. The bases of transistors Q and Q16 assume similarpotentials and, as a consequence, turn off, thereby removing maximumdrive from the motor. At the next cycle of drive power, npn transistorQ12, which is connected in an emitterfollower configuration, couples thevoltage of capacitor C16 (which represents actual motor speed) to thejunction of resistors R44 and. R35 and also'to the base of npntransistor Q10 and pnp transistor Q9. Resistors R31 and R30 provide avoltage potential which represents the desired regulated low speed. Thispotential is monitored when the plus power supply and the minus powersupply are at maximum voltage. When the desired low speed voltagepotential is generated, it is compared with the voltage potential at thejunction of resistors R44 and R35 to determine whether actual motorspeed is greater than, less than, or equal to the .desired regulated lowspeed. Assume that the actual motor speed is greater than the desiredregulated low speed. This will cause transistor Q10 to turn on (sincethe base-emitter is forward biased) providing drive to the base of pnptransistor 011. Thus, transistor Q11 is biased on and provides drive tothe base of npn transistors Q21 and Q22 through resistor R37. Thiseffects maximum braking using the dynamic characteristics of the DCshunt field motor M1. This process is repeated during subsequent cyclesof the plus and minus power supply until such time as the voltagereflected at the juncture of resistors R44 and R35 is similar to thevoltage reflected at the juncture of resistors R31 and R30, indicatingthat the motor speed is at the desired value. Subsequent reduction inthe motor the positive potential as seen at the juncture of R31 and R30will be conducted through resistor R34 to the emitter of pnp transistorQ9. The potential at the base of Q9 will be slightly less than thepotential at the emitter and therefore Q9 will turn on and provide drivefor npn transistor Q8 which will in turn provide drive through resistorR219 to pnp transistor Q19. This drive will be proportional to thedifference between the actual speed and the desired motor speed. As aconsequence, when the motor speed falls below the desired speed, motordrive will occur. Throughout the operation of the motor speed regulator,when the positive power supply goes to 0, transistor Q24 saturatessupplying the voltage generated by the motor to capacitors C17 and C16such that these two capacitors always maintain a representation of theactual motor speed. As may be seen, regardless of the mechanicalresistance of the load being driven by the motor, the speed of the motoris accurately regulated.

A logic zero at input A is coupled through resistor R54 to the base ofQ29 to initiate a programmed stop of the motor at a precise location.The logic zero biases Q29 to the off condition. The voltagerepresentative of actual motor speed, as seen on capacitor C17, isapplied to the base of NPN transistor Q25. Transistor Q25 and resistorR64 provide a voltage to current convertor. Increases in the voltage onthe base of Q25 provide increases in the voltage on the emitter and,consequently, an increase in current through R64. Since emitter currentis approximately equal to collector current, the current through thecollector is a function of the voltage on the base. Resistor R207provides an increase in the collector current as a function of anincrease in the power supply voltage, effecting a slightly higherrepresentation of motor speed for higher power supply values. TransistorQ26 and resistors R62 and R63 provide an additional current to voltageconversion stage. Resistor R63 converts the current from transistorQ25-to a voltageand resistor R62 converts this voltage back to acurrent. The reason for using this subsequent stage is to amplify thevoltage and current levels for more effective operation with transistorQ29, capacitor C19 and transistor Q28. The current from transistor Q26is applied to capacitor C19 so that the voltage on C19 is the integralof the current. Since current is proportional to motor speed, thevoltage on C19 is proportional to the integral of motor speed or inother words, distance of motor rotation. After a predetermined delay ormotor rotation, the voltage at C19 increases to a value larger than thevoltage at the wiper of potentiometer R56, biasing transistorQ28 on andsubsequently turning on NPN transistor Q30. As Q30 turns on, a logic 0will be seen at resistor R53. As-

. suming a logic 1 is still reflected at input B, transistors Q13 andQ14 will saturate. This will provide drive through resistor R50 to PNPtransistor Q17. This will saturate transistor Q17 which willsimultaneously provide drive for transistors Q10 and Q11. This isaccomplished by the collector of Q17 supplying drive through resistorR44 to the base ofQ10 and the emitter of Q17 supplying drive throughresistor R32 to the base of imum braking of the motor and an immediatestop.

The operation of NPN transistor Q20 is to prevent any possibility ofdynamic braking during full speed operation. During full speedoperation, transistors Q and Q16 are saturated. This enables transistorQ20 to become saturated and thereby prevents any input from occuring attransistor Q21.

Transistors Q5 and Q6 and associated circuitry provide a conventionalmultivibrator. The operation of the multivibrator is to divide the 120Hzfrequency occuring on the power supply and provide an input totransistor Q7. The effect of the multivibrator is to enable transistorQ8 to drive the motor only on alternate cycles. This ensures thatsufficient time is available for transistor Q24 to supply a voltagerepresenting the speed of the motor to capacitor C17. Otherwise, themotor time constants may impede proper operation of the circuit.

In the data retrieval and display systems previously described ingeneral and described in more detail hereinafter, the DC motor controlcircuit of the present invention may be utilized to control operation ofthe rotary storage file. The control circuit would operate the rotaryfile at maximum speed until a desired microfische was selected. Therotary file would then be stopped so that thedesired microfische wasaccurately located in a preselected position for retrieval.

A more detailed description of the data retrieval and display systemabove described and circuits that may be utilized therein may be foundin copending application Ser. No. 104,038, filed 1-5-71, entitledAutomatic Data Retrieval and Display System", filed concurrentlyherewith and assigned to the same Assignee.

An illustrative embodiment of the DC Motor Control circuit of thepresent invention has been described herein. It willbe appreciated,however, by a person skilled in the art that various modifications tothe details of construction may be made without departing from the scopeof the invention.

What is claimed is: I V

l. A d.c. motor control circuit for driving a motor at selectable speedsand stopping the motor at a precise position comprising in combination:

a. logic input means for controlling operation of said d.c. motor; 1

b. sources of plus and minus full wave rectified unfiltered drive power;

c. circuit means for connecting said drive power to said motor inresponse to a first logic signal at said input means for driving saidmotor at maximum speed; 7

d. speed regulator means responsive to a second logic signal at saidinput means for driving said motor at preselected low speed; and

e. integrator means responsive to a third logic signal at said inputmeans for converting motor speed into motor rotation distance, saidintegrator means controlling the time at which dynamic braking isapplied to said d.c. motor to stop motor operation at a precisepredetermined position.

2. A DC motor control circuit as set forth in claim 1 wherein said speedregulator means comprises:

a. speed sensing means for providing a first voltage proportional to theactual speed of said motor during low voltage portions of saiddrive(power; and b. detection means for comparing sai first voltage witha second voltage proportional to a preselected low speed, said detectionmeans selectively applying power for dynamic braking action as requiredto regulate the speed of said motor to correspond with said preselectedspeed.

3. A d.c. motor control circuit as set forth in claim 2 wherein saidspeed sensing means comprises a transistor and at least one capacitorconnected in series across the armature of said motor, the base of saidtransistor being electrically connected to one terminal of said armatureby resistor means, the emitter of said transistor being connected to theother terminal of said armature and the collector being coupled to saidone terminal by capacitor means wherein said transistor is biased intoconduction by said resistor means during low voltage portions of saiddrive power, said capacitor means being operative to store said firstvoltage proportional to the actual motor speed.

4. A d.c. motor control circuit as set forth in claim 2 wherein saiddetection means comprises means for generating said second voltageproporational to said preselected low speed and transistor means forcomparing the amplitude of said first and second voltages, saidtransistor means effecting operation of dynamic braking means when saidfirst voltage is larger and applying drive power to said motor when saidsecond voltage is larger.

5. A d.c. motor control circuit as set forth in claim 4 wherein saidmeans for generating said second voltage comprises a voltage dividerresistor circuit connected across said negative and positive powersupplies.

6. A d.c. motor control circuit as set forth in claim 4 wherein saiddynamic braking means comprise a transistor connected directly acrossthe armature of said d.c. motor, said transistor when biased oneffectively shunting the armature of said motor to effect dynamicbraking thereof.

. 7. A d.c. motor control circuit as set forth in claim 1 wherein saidintegrator means comprises in combination a voltage to currentconversion circuit, said circuit converting a voltage proportional toactual motor speed into a current proportional to actual motor speed,and capacitor means for storing said current, the

voltage of said capacitor means effectively representing the integral ofsaid current, said capacitor voltage being proportional to distance ofrotation of said motor and being operable to provide an enable signal toeffect dynamic braking after a predetermined distance of motor rotationto thereby accurately stop said motor rotation at a precisepredetermined location.

8. A motor control circuit as set forth in claim 7 wherein said voltageto current converter comprises a transistor and resistor circuit, avoltage proportional to actual motor speed being applied to the base ofsaid transistor to vary the current flowing through said resistor inproportion to the amplitude of said voltage.

1. A d.c. motor control circuit for driving a motor at selectable speedsand stopping the motor at a precise position comprising in combination:a. logic input means for controlling operation of said d.c. motor; b.sources of plus and minus full wave rectified unfiltered drive power; c.circuit means for connecting said drive power to said motor in responseto a first logic signal at said input means for driving said motor atmaximum speed; d. speed regulator means responsive to a second logicsignal at said input means for driving said motor at preselected lowspeed; and e. integrator means responsive to a third logic signal atsaid input means for converting motor speed into motor rotationdistance, said integrator means controlling the time at which dynamicbraking is applied to said d.c. motor to stop motor operation at aprecise predetermined position.
 2. A D.C. motor control circuit as setforth in claim 1 wherein said speed regulator means comprises: a. speedsensing means for providing a first voltage proportional to the actualspeed of said motor during low voltage portions of said drive power; andb. detection means for comparing said first voltage with a secondvoltage proportional to a preselected low speed, said detection meansselectively applying power for dynamic braking action as required toregulate the speed of said motor to correspond with said preselectedspeed.
 3. A d.c. motor control circuit as set forth in claim 2 whereinsaid speed sensing means comprises a transistor and at least onecapacitor connected in series across the armature of said motor, thebase of said transistor being electrically connected to one terminal ofsaid armature by resistor means, the emitter of said transistor beingconnected to the other terminal of said armature and the collector beingcoupled to said one terminal by capacitor means wherein said transistoris biased into conduction by said resistor means during low voltageportions of said drive power, said capacitor means being operative tostore said first voltage proportional to the actual motor speed.
 4. Ad.c. motor control circuit as set forth in claim 2 wherein saiddetection means comprises means for generating said second voltageproporational to said preselected low speed and transistor means forcomparing the amplitude of said first and second voltages, saidtransistor means effecting operation of dynamic braking means when saidfirst voltage is larger and applying drive power to said motor when saidsecond voltage is larger.
 5. A d.c. motor control circuit as set forthin claim 4 wherein said means for generating said second voltagecomprises a voltage divider resistor circuit connected across saidnegative and positive power supplies.
 6. A d.c. motor control circuit asset forth in claim 4 wherein said dynamic braking means comprise atransistor connected directly across the armature of said d.c. motor,said transistor when biased on effectively shunting the armature of saidmotor to effect dynamic braking thereof.
 7. A d.c. motor control circuitas set forth in claim 1 wherein said integrator means comprises incombination a voltage to current conversion circuit, said circuitconverting a voltage proportional to actual motor speed into a currentproportional to actual motor speed, and capacitor means for storing saidcurrent, the voltage of said capacitor means effectively representingthe integral of said current, said capacitor voltage being proportionalto distance of rotation of said motor and being operable to provide anenable signal to effect dynamic braking after a predetermined distanceof motor rotation to thereby accurately stop said motor rotation at aprecise predetermined location.
 8. A motor control circuit as set forthin claim 7 wherein said voltage to current converter comprises atransistor and resistor circuit, a voltage proportional to actual motorspeed being applied to the base of said transistor to vary the currentflowing through said resistor in proportion to the amplitude of saidvoltage.